Stepping motors and switches



May 9, 1961 J. P. WATSON STEPPING MOTORS AND SWITCHES 5 Sheds-Sheet 1Filed May 28, 1957 JAMES P. WA TSON,

IN VEN TOR.

HERZ/G 8 JESS UP,

ATTORNEYS.

May 9, 1961 J. P. WATSON 2,983,798

STEPPING MOTORS AND SWITCHES Filed May 28, 1957 5 Sheets-Sheet 2 JAMESP. WA TS ON,

IN VEN TOR.

HERZ/G 8 JESSUP,

ATTORNEYS- ZAMM TM y 1951 J. P. WATSON 2,983,798

STEPPING MOTORS AND SWITCHES Filed May 28, 1957 5 Sheets-Sheet 3 if 6)JAMES R WATSON,

INVENTOR. HEIPZ/G a JESSUP, v Jig. 3 A TTORNEKS.

May 9, 19 1 J. P. WATSON STEPPING MOTORS AND SWITCHES 5 Sheets-Sheet 4Filed May 28, 1957 y 44 vx M f SR.SV Hm? m m .VZT ma r E H m m. J H Yd Bwm\m%\\%\ y 1961 J. P. WATSON 2,983,798

STEPPING MOTORS AND SWITCHES I Filed May 28, 1957 5 Sheets-Sheet 5 JAMESP. WATSON,

INVENTOR.

HEPZ/G 8 JESSUP 18 BY ATTORNEYS.

United States Patent Ofiice 2,983,798 Patented May 9, 1961 STEPPINGMOTORS AND SWITCHES James P. Watson, Whittier, Calif. (59 Waterway Road,Waterway Village, Jupiter, Fla), assignor of one-half to Joe Davidson,South Gate, Calif.

8 Claims. (Cl. 200-1) This invention relates to stepping motors andswitches, and more particularly to certain advantageous features of acombined stepping motor and rotary switch.

It is an object of this invention to provide an improved switchespecially adapted for use with a rotary stepping motor.

In a sliding brush type of contact, where the brush rides alternatelyand successively against a contact segment and thence against aninsulation segment, there is a perennial problem occasioned by the factthat the brush drags tiny particles of insulation across and into theface of the contact segment, and also into its own face, therebyincreasing the contact resistance, with consequent arcing and pitting,which further aggravates the problem.

It is an object of this invention to provide in a sliding brushstructure of the above type, means for obviating this dispersal ofinsulating particles into the conducting contact face.

It is another object of this invention to obviate, in a switch meansembodying a sliding brush, the inherent problem of having the brushaccumulate tiny bits of insulation into its face or surface.

It is a further object of this invention to provide in such a switchstructure, means for coping with the uneven wear between the insulationand the conducting contact segments, which ultimately causes the brushto ride up and down in an undulatory fashion with resulting danger ofbrush bounce, and consequent arcing and pitting.

It is another object of this invention to eliminate undesirable brushbounce, such as would or might result from some accelerations or shocks,either internal or external, in a switch structure.

It is another object of this invention to provide an improved slip ringand commutating segment brush structure of simplified and sturdyconstruction,

it is a further object of this invention to provide improved means forsealing a casing or housing where a cross-member such as a conduit orconductor passes through the wall of the housing.

It is a further object of this invention to provide an improved assemblymeans for a casing or a housing involving an improved assembly dowel.

It is a further object of this invention to provide an improved assemblydowel which inherently and resiliently holds two parts of a housingtightly together.

It is another object of this invention to provide an improved assemblydowel which does not have to be held during the turning of a screw ornut.

It is a further object of this invention to provide an improved assemblydowel which has a non-turning head, thereby obviating the requirementfor a screwdriver or wrench to hold one end of the dowel, which headalso serves as a mounting pad, and as a socket or nut to receive amounting screw.

It is a further object of this invention to provide an assembly dowelwhich simultaneously has a non-circular head preventing turning of oneend of the dowel, which places the tWo parts of a casing to be assembledin resilient tight engagement, in which the head serves as a mountingpad, and in which the head also receives a mounting screw.

It is a further object of this invention to provide an assembly dowelhaving incorporated therein means for inhibiting turning of a mountingor assembly screw threaded into either end of the dowel.

In accordance with these and other objects which will become apparenthereinafter, preferred forms of the present invention will now bedescribed with reference to the accompanying drawings wherein:

Figure 1 is a longitudinal sectional view of a stepping motor and switchembodying features of the present invention;

Figure 2 is a cross-section taken on a line 2--2 of Figure 1;

Figure 3 is a fragmentary perspective view of a brush support structureand brushes embodied in the stepping switch portion of the assembly;

Figure 4 is a fragmentary partially sectioned elevation of a brushstructure embodying features of the present invention;

Figure 5 is a fragmentary end view with parts broken away showing thebrush structure in one position of operation;

Figure 6 is a cross-section taken on a line 6-6 in Figure 1;

Figure 7 is a fragmentary sectional view taken on a line 7-7 of Figure6;

Figures 8 and 9 are perspective views taken from different angles, of astop pawl shown in Figure 6;

Figure 10 is a fragmentary exploded perspective view of a driving pawlshown in Figure 6;

Figure 11 is an exploded perspective view of the rotor and shaft of thepresent invention;

Figure 12 is a longitudinal sectional view of a dowel, taken along line1212 of Figure 2;

Figure 13 is a similar view showing a modified form of dowel for holdingthe casing of the stepping motor and switch together;

Figure 14 is a cross-section taken on line 14-14 in Figure 13;

Figure 15 is an end view partially sectioned showing another form ofbrush structure especially adapted for a combination slip ring andcommutator assembly;

Figure 16 is a fragmentary section showing the brush structure of Figure15;

Figure 17 is a fragmentary elevation showing a modified form of balljoint support for the brush structure of Figures 15 and 16;

Figure 18 is a fragmentary sectional view of the brush of Figure 17;

Figure 19 is a fragmentary end elevation partially sectioned of anotherform of contact structure;

Figure 20 is a fragmentary section taken on line 20- 20 of Figure 19;

Figure 21 is a fragmentary view taken in the same plane as Figure 2 andshowing a modification embodying the sealing ring feature of the presentinvention; and

Figure 22 is a fragmentary section taken on line 2222 in Figure 21.

Referring to the drawings, and particularly to Figures 1 and 2, there isillustrated a cylindrical casing 31 formed of a plurality of abuttingcylindrical sections 32, 33, 34 and 35. An end wall 37 formed integralwith the section 32 closes the left end of the casing 31, and an endwall 38 closes the right end of the casing. Spanning the end walls 37and 38 and journalled therein by bearings 39 and 41, is a shaft 42, overwhich is journalled a para magnetic rotor 43. The rotor 43 includes anon-magnetic bushing 45 pressed therein, which is journalled over theright-hand portion 46 of the shaft 42. The rotor 43 is surrounded by acircumjacent coil 44, which when energized with an electric current,produces an axial flux in the rotor 43. The coil 44 is pressed into thecylindrical casing section 34 and abuts against a transverse wall 50,which has an opening 47 to permit passage of the rotor 43.

Axial flux in the rotor 43 leaves the rotor by means of radial poles 48,which project radially outward into proximity with a pair ofcomplementary stationary poles 49 formed integral with the cylindricalcasing section 35.

Whenever the coil 44 is energized, the magnetism in the poles 48 causesthem to attempt to align with the stator poles 49. This effects rotationof the rotor 43, which is stopped in the position shown in the Figure 6by a balanced stop pawl 51 pivoted to the end wall 38 by a pivot pin 52passing centrally through the pawl 51. The innermost end of the pawl 51is formed with a tooth 53 which engages one of a plurality of teeth 54formed around a disc 56 secured firmly to the shaft 42.

The disc 56 is pushed around by a drive pawl 57 pivoted at its center bya pin 58 to the rotor 43. A tooth 59 at the inner end of the pawl 57engages the disc 56 to push it around through an arcuate stroke of therotor 43.

At the start of the rotor stroke, the tooth 53 is held out of engagementwith the disc 56 by a pin 61 extending outwardly from the transverseface of the rotor 43, which engages a cam surface 62 formed integralwith, and extending laterally from, the pawl 51. As the stroke of therotor 43 progresses, the pin 61 departs from the cam surface 62,allowing a torsion spring 63 to bias the pawl 51 counterclockwise, sothat the tooth 53 is in position to engage a tooth 54 and'thus stop theshaft 42 and bring to a halt the forward arcuate excursion of the rotor43.

When the coil 44 is de-energized, the rotor 43 moves backcounterclockwise (Figure 6) under the bias of a torsion spring 64disposed in a circular groove 66 formed in the interior face of the endwall 38. One end of the spring 64 projects into an anchor hole 67 formedin a stop member 68 projecting from one of the poles 48, and the otherend of the spring 64 is secured to the end wall 38. The counterclockwiserelaxation stroke of the rotor 43 is stopped by engagement of the stopmember 68 with a complementary stop member 71 projecting inwardly fromthe end wall 38. As the rotor 43 oscillates back counterclockwise, thedrive pawl 57 pivots out of the way by the action of a cam surface 72formed on the inner face of the tooth 59 and the tooth 54 on the disc56. The tooth 59 then drops back into a space between disc teeth underthe influence of a torsional biasing spring 73.

As best seen in Figures 6 and 10, the center portion of the spring 73resides in a diametrical kerf 74 formed in the end of the mounting pin58. Emerging from the kerf 74, each end of the spring 73 wraps aroundthe pin 58 in a circumferential groove 76 and then departs tangentiallyfrom the pin 58 and is turned under a ledge 77 formed integral with thedrive pawl 57. As the pawl 57 rocks back and forth in operation of themotor, the wrap-around portion of the spring '7 3 flexes back and forthto provide the necessary biasing torsion. It will be noted that all ofthe pawls shown in Figure 6 are completely balanced structurally, sothat any accelerative forces such as might result from a sudden shock onthe equipment are fully balanced and have no effect on the pawls,tending to drive them neither forward nor back in their engagement withthe disc 56.

A holding pawl 78 similar to the drive pawl 57 is also pivotally mountedto the end wall 38 and serves to prevent the disc 56 from beinginadvertently driven in the wrong direction, i.e. counterclockwise.

When the rotor 43 drops back to its relaxed position uponde-energization of the coil 44, the disc 56, and hence the shaft 42, canmove only in one direction, namely clockwise, which it does upon thenext subsequent energization or pulsing of the coil 44.

The coil 44 is maintained pressed against the interwall 50 by acorrugated washer 81 pressed between the coil 44 and the inwardlyextending stationary poles 49 of the casing section 35. The washer Si isnot a complete ring, being cut oil and turned laterally to form tabs 82at each end, which hook around the ends of the poles 49. This leaves afree area into which the leads 83, that provide electrical current forthe coil 44, may be brought.

The shaft 42 projects leftward beyond the rotor 43 into the left-handportion of the casing 31 and there serves to actuate one or more rotaryswitches contained within the single casing 31. In .the presentinstance, two such switches are shown, one being mounted in the casingsection 32, and the other in the end casing section 33. Each rotaryswitch, for example, the switch 84 consists of a non-conductive bushing86 splined at to the lefthand end 88 of the shaft 42. Splined in turnover the bushing 86 is a conductive balanced switch arm 87, which servesas a brush support means for a pair of opposed conductive brushes 89 and90. Each brush, for example the brush 89, is rotatably mounted orpivoted at its center to the operating arm 87 by means of an arbor 91over which the brush is journalled.

The brush 89 bears outwardly into sliding electrical engagement with aplurality of contact members in the form of commutator segments 92spaced around a circular path centered at the shaft 88. The segments 92are embedded in a non-conductive ring 93 secured, as by pressing, intothe cylindrical casing section 33. In this manner the casing 33 forms aframe means for mounting or supporting the contact members 92 in acircular path, and the brush support arm 87 constitutes a carrier formoving the brush 89 around the same circular path, so that the brush 89comes successively and repetitively in engagement with the variouscontact members 92.

Spaced axially from the ring of segments 92 and also mounted in theinsulating member or ring 93 is a solid conducting ring 94 havingsubstantially the same internal diameter as the circle or ring formed bythe internal surfaces of the contact segments 92. The ring 94 is engagedby an opposite brush 9% in a manner similar to the engagement of thebrush 89 and the segments 92, except that the brush is in constantengagement with the ring 94, whereas the segments 92 are separated byintervals of circumferential space.

The circumferential regions between the segments 92 are depressed withrespect to the surface of the segments 92 by being formed of a somewhatlarger diameter, as best seen in Figure 2.

During the interval when the outer, engaging face of the brush 89 is notin engagement with a contact member or segment 92, it is prevented frommoving outward into engagement with the insulation 93 by a laterallyprojecting guide pin 96 formed integral with the brush 89. The guide pin96 engages an insulating rail 97 projecting inwardly from, and axiallypositioned between, the ring 94 and the circle or discrete contactsegments 92. In all positions of the brush 89 where the brush face 98 isin engagement with a contact segment 92, the rail 97 is relieved, asshown at 99, so as to allow unhampered bearing of the brush against thecontact segments. Similarly, in those positions of the brush 89 wherethe brush face 98 is opposite the insulation 93-, i.e. between segments92, the laterally spaced projecting pin 96 bears against the rail 97,thereby keeping the face 98 spaced from the insulation 93. In thismanner, the brush face 98 is kept out of contact with the spacinginsulation 93, and there is thus obviated the troublesome problemsoccasioned by the dragging of tiny particles of insulation over and intothe face of the contact segments or the brush. The rail surfaces 97 areso related to the engaging faces of the contact segments 92 that theguide pin 96 comes into engagement with the rail 97 just before assspssthe brush face 98 leaves the contact segment 92, and the brush face 98'comes into engagement with the next successive segment 92 just beforethe guide pin 96 leaves the rail 97.

The brush 89 is torsionally biased so as to urge the face 98 outwardlyinto engagement with the contact segments 92 (and the guide pin 96 intoengagement with the rail 97), by means of a torsion spring 101, whichalso serves as a securing member for mounting the brush 89 to the studshaft 91. The torsional mounting of the brush 89 by the torsion spring101 is substantially the same as the torsional mounting of the pawl 57by the spring 73, as best seen by a brief comparison between Figures 3and 10. Both the brushes 89, 90 and the pawls 57, 51, 78, are of abalanced mounting construction so as to be unafiected by shock or otheraccelerative forces.

Electric current is carried to the segments 92 from the collector ring94 through the brushes 90 and 89' and the conducting brush support arm87. To insure good electrical contact between the brushes and the arm87, a flexible shunt 102 may be laid in the kerf 103 formed in the headof the mounting stud 91 before insertion of the mounting torsion spring101. The center of the shunt 102 is spot-welded to the bottom of thekerf 103 and the ends are in turn spot-welded to the brush 89.

As best seen in Figure 5, the lateral guide pin 96, by riding on therail 97, keeps the brush 89' completely free from engagement with anypart that is fixed to the casing 31, except the circle of contactsegments 92, thereby preventing dragging of insulation particles intothe contacts or brush, and the dragging of conducting particles into theinsulation.

As best seen in Figures 1 and 2., the several conductors 19 4 arebrought radially directly into bond with the contact segments 92,passing through the casing 31 at the circumferential joint between thetwo casing sections 33 and 34. At this joint, the opposed end faces ofthe sections 33 and 3 are provided with complementary semicirculargrooves 106, which when placed together form a complete bore for thepassage of the conductors 104. The lead or conductor for the single ring94 is brought into the casing at the same plane as the leads 104, asshown at 107 in Figure 2, and then is turned at rightangles and passesthrough the rail 97 (which also serves as an insulating wall between thering 94 and the ring of segments 92). This structure is shownlongitudinally for the conductor 108 of the switch section 109, that issubstantially identical to the switch section 84 previously described.

In order to inhibit axial play of the parts mounted on the shaft 42-, asnap ring 111 is secured in a groove 112 in the shaft 42, between thetwo sections 88 and 46. The several bushings corresponding to thebushing 86 of the switch section 84 are then butted end to end and heldaxially and resiliently by an offset resilient spring washer 119, theoutermost end of which bears against the bearing 39' in the end wall 37.The stator parts, i.e. the insulating rings corresponding to the ring 93are kept axially pressed into place by a corrugated spring washer 113similar to the shaft spring washer 110 previously described.

In operation, each pulse of current applied to the coil 44 causes theshaft 42 to step through an arc of 36 (clockwise in Figure 6,counterclockwise in Figure 2), and this transfers the brush 89 from onecontact segment 92 to the next succeeding segment. Thus a voltage orother signal applied to the conductor 107 is successively distributed tothe several commutator conductors 194 of the switch 84. The switch means109 is similarly stepped around its successive contact segments.

As will be best seen in Figure 1, the stepping motor generally, andparticularly the casing 31, consists of a plurality of cylindricalsections which are held together by three longitudinal dowels (116,Figure 2) which reside in ears 115 projecting radially from the casing31.

Each elongate dowel 116 has a spiral slit 117 extending substantiallythe full length of the dowel. In the embodiment shown in Figure 12, theslit 117 is given an appreciable width, for reasons which will beexplained hereinafter, to form actually a slot. It is preferred toprovide the dowel 116 with an axial bore extending through the lengththereof, so that the dowel becomes in effect a tube, and the slit 117extends through the wall of the tube to communicate with the bore 118,for substantially the full length of the slit 117.

The dowel 116 is made of a resilient material such as steel, so thatwhen it is placed under tension, the slit 117 permits the dowel tostrain appreciably thereby providing an unusually wide latitude ofexpansion and contraction of the assembly, without loosening.

The dowel 116 is placed under tension by an integral head 119 formed onthe right-hand end of the dowel 116, and the head 121 of an assemblyscrew 122 which is threaded into threads 123 on the left-hand end of thebore 118. The two heads 121 and 119 press against the respective endmembers or walls 37, 38 and serve to hold the casing 31 togetherlongitudinally and under a resilient force. The dowel head 119 is formedwith a fiat 124, which resides against a corresponding flattened surface126 formed on the end plate 38. This prevents the dowel 116 from turningas the screw 122 is screwed into place by means of a wrench insertedinto a hexagonal socket 127.

At the right-hand end, the bore 118 is also threaded to receiveamounting screw 12% that secures the stepping motor to a mounting membersuch as a plate 129. The head 119 extends slightly beyond the surface ofthe end wall 38 as shown in Figure 12, to form a mounting pad. The threedowels thus constitute not only assembly means for the casing 31, butalso form three equally spaced mounting pads by means of which thestepping motor may be mounted to an uneven base without distortion ofthe case.

In the embodiment shown in Figure 12, both of the screws 128 and 122have right-hand threads, and the slit or slot 117 is also right-hand.Thus, as the screws 122 and 1 23 are screwed into place there is atendency to unwind the spiral and thereby facilitate insertion of thescrews. Conversely, any attempt on the part of the screws 122 or 128 towork themselves out by unscrewing is resisted by a tightening action ofthe spiral around the screws. It is for this reason that the slits 117are given a slight width, so that there is operating room for the spiralto effect a tightening action around screws.

(Note that slit 117 is of the same hand as the screws 128 and 122,namely right-hand.)

In Figure 13, there is shown a modified form of dowel 131 having a slit132 formed therein which is of no appreciable width; that is to say,when the tube forming the dowel 131 is unstressed, the walls of the slit132 touch each other. As in the dowel shown in Figure 12, the threadsformed in each end of the tube 131 are of right-hand, but it will benoted that the slit 132 is of lefthand.

Like the dowel 116, the dowel 131 is also placed under resilient tensionby the screwing in of the assembly screw 133. Since the slit 132 is ofopposite hand than the threads in the end of the tube, there is atendency for the spiral tube to wrap itself tightly around the screws asthey are screwed into the tube. However, this tendency is blocked by thefact that the slit 132 has no appreciable width, and therefore the tubecannot ensmall appreciably as the screws are threaded in.

The dowel 131 is somewhat more rigid than the dowel 116, and thuspermits a closer and tighter fit in the casing 31.

To inhibit the screws in the end of the dowel from coming loose, theedge of the slit 132 is dimpled inwardly as shown at 134 to form aprojection that fn'ctionally engages the screw threads and inhibitsunscrewing thereof.

Another form of 1 brush structure embodying the balancedacceleration-proof characteristic of the brush 89 is shown in Figuresand 16. In Figure 15, the casing 136 constitutes a frame for supportinga pair of ring structures 137 and 138. The ring structure 138 is ofinsulating material and has embedded therein a plurality of inwardlyfacing contact segments 139 which are successively engaged by one arm141 of a brush 142. The ring structure 137 is of insulating material andsupports a continuous conducting ring 143 having an internal diametersubstantially the same as the internal diameter formed by the innersurfaces of the several contact segments 139. Sliding against theinternal face of the ring 143, is a corresponding arm 144 of the brush142.

The brush 142 is universally mounted to a brush support 146 which iskeyed to and rotated by the shaft 147. This universal mounting iseffected by means of a ball 148 formed on the end of a projecting post149 secured to the brush support 146.

The two arms 141 and 144 are biased into sliding engagement with theirrespective stationary ring structures by means of a spring wire 151bearing against the brush in a longitudinal bore 152 and passingcentrally through a bore 153 formed in the ball 148. The ball 148resides in a socket 154 formed centrally in the brush 142.

With the structure shown, the brush 142 is free to rock back and forthlaterally, thereby maintaining even pressure against the two ringstructures 139 and 143.

If desired, the bias of the brush 150 may be fortified by wrapping thebiasing spring 156 around the ball 145 in the manner shown in Figure 18.The wrap-around portions of the spring 156 resides in a groove 157 (Fig.17) formed in the ball 145 and the two bores 158 and 159 are obliquelyformed in the brush 150 as shown in Figure 18. The flexing action of thespring 156 is generally similar to that of the spring 73 describedhereinbefore in connection with Figure 10.

Another form of the present invention embodying the balanced contactstructure is shown in Figures 19 and 20. In this figure, the insulatingcasing 161 constitutes a frame for holding a plurality of individualcontact segments 162 each of which has associated therewith its owncontact arm 163 balanced and pivoted at the center thereof by means ofan arbor 164. The arbor 164 is secured to and projects laterally from amounting plate 166 having a projecting tab 167 through which extends astranded conductor 168 which is welded or soldered thereto at 169.

The arm 163 is torsionally biased by a spring 171 which urges the movingcontact 172 on the am 163 into contact with the contact segment 162. Theopposite or inner end of the arm 163 is formed with a boss 17 3 which isactuated by a cam 174 keyed to and rotated by the shaft 176. As the earn174 rotates, a depressed portion 177 on the periphery thereof comesopposite the successive bosses 173, allowing that particular switch arm163 to make contact with the contact 162 and thereby close a circuitbetween the conductor 168 and the conductor 178 of that particularswitch structure.

As in the other embodiments described, this switch too has the advantagethat it is virtually free from being affected by shock and otheraccelerations, because all moving parts are balanced against shock andtherefore against contact bounce due to external forces.

In order to seal two adjacent cylindrical casing sections, as forexample 32 and 33, to each other, and also seal them to the variousconductors 104 where the conductors enter the casing, a sealing ring 180constructed in accordance with the present invention is illustrated inFigures 21 and 22. This ring consists of a major ring 181 made of pliantmaterial and formed about a major axis which coincides with the axis ofthe shaft 42. At each point where a conductor 108 is to penetrate thecasing 31, a minor ring 182 is formed in the major ring 181 and made ofdiameter appreciably smaller than the diameter of the major ring. Theminor ring is disposed substantially on the surface of an imaginarycylinder formed about the major axis, i.e. the shaft 42.

The internal diameter of the minor ring 182 is made slightly smallerthan the external diameter of the lead 104, so as to grippingly engagethe lead as it passes through the minor ring 182.

Each of the opposed end faces of the joined cylindrical casings 32 and33 is formed with complementary semicircular cross bores 183, whichtogether form a single circular bore for reception and passage of thelead 104. Grooves 184 and 186 are formed in the respective end faces oredges of the cylinders 32 and 33, and extend continuously around thefaces including the faces of the semi-circular bores, as shown at 187 inFigure 22.

Where the lead 104 passes through the wall of the casing 31, theinterspace between the strands of the conductors is filled with solderas shown at 190 in Figure 22.

The relative dimensions of the pliant ring or sealing member and thegrooves 184 and 186 are such that all portions of the pliant ring 180are compressed as the two sections 32 and 33 are drawn tightly intoengagement with each other by tightening action on the several dowels116.

In this way, the single sealing member 180 serves the double function ofsealing the cylindrical casings 32 and 33 to each other, and also to theseveral leads or conductors 104 where they enter the casing 31.

While the instant invention has been shown and described herein in whatis conceived to be the most practical and preferred embodiments, it isrecognized that departures may be made therefrom within the scope of theinvention, which is therefore not to be limited to the details disclosedherein, but is to be accorded the full scope of the claims.

What is claimed is:

1. Brush structure comprising frame means, brush support means, meansfor mounting said frame means and said brush support means for movementrelative to each other along a predetermined path, brush means movablymounted to said support means and movable with respect tosaid framemeans along said path, a contact member mounted to said frame means andengageable by a face of said brush means during a portion of therelative movement between said brush means and said frame, rail meansmounted to said frame means along the remainder of said path of relativemovement, guide means spaced from said face and fixed with respect tosaid brush means for engaging said rail means over that portion of saidpath of relative movement during which said brush means is not inengagement with said contact means, and means for biasing said brushmeans toward said contact means.

2. Structure in accordance with claim 1 wherein said face -is completelyfree of engagement from any part that is fixed with respect to saidframe means, except said contact member, thereby relieving said face ofall interengaging surfaces except the interengagement between saidcontact member and said face.

3. Apparatus in accordance with claim 1 wherein said path is circularand said brush support means comprises a member rotatably mounted tosaid frame means.

4. Brush structure comprising frame means, a brush support member, meansfor mounting said frame means and said brush support member for relativerotation, a brush member pivoted at its center to said brush supportmember, a contact member mounted to said frame means and engageable by aface of said brush member during a portion of the relative movementbetween said brush support member and said frame means, rail meansmounted to said frame means, guide means spaced from said face and fixedwith respect to said brush member for engaging said rail means duringthose portions of said relative rotation during which said brush memberis not in engagement with said contact member, and double-torsion springmeans for urging both ends of said brush member in a similar rotativedirection, thereby to bias one end of said brush member against saidcontact member.

5. Apparatus in accordance with claim 4 comprising a plurality ofcontact segments and guide rails spaced alternately around the circularpath on said frame means, whereby said brush face engages said contactsegments and said guide means engages said rail means alternately.

6. Apparatus in accordance with claim 5 wherein said rail means islaterally oflFset from said contact segments with respect to said pathof relative movement.

7. Electrical contact structure comprising: a frame, an electricalcontact member secured to said frame, a rotor pivotally mounted to saidframe, a contact arm balanced and pivotally mounted at the centerthereof to said rotor, one end of said contact arm being engageable withsaid contact member, means for rotationally biasing said said arm aboutits pivotal mounting to resiliently urge said end into engagement withsaid contact member, whereby upon rotation of said rotor, relativemovement between said contact arm and said contact member is effected,thereby to open and close a circuit between said cont act arm and saidcontact member.

8. Electrical contact structure comprising a frame, an electricalcontact member secured to said frame, a rotor pivotally mounted to saidframe, a contact arm balanced and pivotally mounted at the centerthereof to said rotor, the pivot point of said contact arm being spacedappreciably from the pivot axis of said rotor, one end of said contactarm being engageable with said contact member, means for rotationallybiasing said arm about its pivotal mounting to resiliently urge said endinto engagement with said contact member, whereby upon rotation of saidrotor, relative movement between said contact arm and said contactmember is effected, thereby to open and close a circuit between saidcontact arm and said contact member.

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